1. Field of the Invention
The present invention relates to a bulb-shaped fluorescent lamp and an illumination device including the aforementioned bulb-shaped fluorescent lamp, and more particularly to a bulb-shaped fluorescent lamp and an illumination device with improved light quantity rising properties.
2. Description of the Related Art
In recent years, small-sized bulb-shaped fluorescent lamps have been developed generally comparable in size with normal incandescent lamps, and demand for bulb-shaped fluorescent lamps which can be substituted for normal incandescent lamps is increasing.
Due to the improvement of the lamp technique and lighting circuit technique, the efficiency of the bulb-shaped fluorescent lamp is improving. However, due to the surface area of the main unit of the bulb-shaped fluorescent lamp being reduced owing to reduction of the size thereof, the emission bulb readily exhibits high temperature, even in the event that the heat emission value output from the emission bulb is not excessively great. In particular, with the bulb-shaped fluorescent lamp having a structure wherein the emission bulb has been covered with a globe in order to assume an external view similar to normal incandescent lamps, the temperature of the emission bulb can exceed 100° C. Accordingly, with the emission bulbs in which pure mercury has been sealed, the mercury vapor pressure excessively increases within the emission bulb, leading to reduction of light output. Accordingly, a technique has been known wherein with the fluorescent lamp for lighting under high temperature, an amalgam which is an alloy of mercury (Hg) and indium (In), lead (Pb), tin (Sn), bismuth (Bi), or the like, is sealed into the emission bulb so that the mercury vapor pressure is optimally controlled, thereby improving the lighting efficiency (see Japanese Unexamined Patent Application Publication No. 2001-243913 (pp. 2–4, FIG. 1), for example).
With the emission bulb employing such an amalgam, the time period from the start of lighting up to the time at which output light flux quantity reaches the predetermined value is long, i.e., the emission bulb has a disadvantage of poor light quantity rising property. This is because in the event that the temperature of the emission bulb prior to lighting is low, i.e., generally the same as the room temperature, the luminance of the emission bulb is low immediately following turning on due to reduction of the mercury vapor pressure from the amalgam control, and the mercury vapor pressure increases due to the increase of the temperature of the emission bulb, and accordingly, the luminance gradually increases. As a method for improving the light quantity rising property, a technique has been proposed wherein an auxiliary amalgam formed of indium (In) or the like are provided around the filament electrode thereof so as to compensate for the shortage of the mercury vapor pressure immediately following the start of lighting (see Japanese Unexamined Patent Application Publications Nos. 60-146444 (p. 2, FIGS. 3 and 4) and 11-233065 (pp. 2–3, FIG. 1), and Japanese Examined Patent Application Publication No. 3262168 (pp. 2–6, FIG. 5), for example).
On the other hand, a bulb-shaped fluorescent lamp is known wherein a cooling portion is provided to a part of the emission bulb for improving the light quantity rising property without using an amalgam for controlling the mercury vapor pressure (see Japanese Unexamined Utility Model Registration Application Publication No. 61-63759, for example).
With the aforementioned conventional technique, the cooling portion is provided to a part of the emission bulb, and accordingly, there is no need to use an amalgam, and high mercury vapor pressure can be maintained within the emission bulb even in the event of a low temperature state when the lamp is turned off. That is to say, while the lighting device and the emission bulb is encased within a practically airtight envelope, and accordingly, the internal temperature increases within the envelope, the space within the envelope is separated into a lighting-device space and an emission bulb space by a partition so as to prevent the internal temperature from exceeding a predetermined temperature. Furthermore, an exhaust pipe disposed to the end of the emission bulb for sealing is extended to the lighting device space by 5 through 20 mm so that the temperature of the exhaust pipe is relatively low when the lamp is turned on, whereby the aforementioned cooling portion can be formed at this position.
On the other hand, with the bulb-shaped fluorescent lamp including both of the principal amalgam and the auxiliary amalgam as shown in the aforementioned Japanese Unexamined Patent Application Publications Nos. 2001-243913 (pp. 2–4, FIG. 1), 60-146444 (p. 2, FIGS. 3 and 4), and No. 11-233065 (pp. 2–3, FIG. 1), and Japanese Examined Patent Application Publication No. 3262168 (pp. 2–6, FIG. 5), the mercury migrates from the principal amalgam to the auxiliary amalgam until achieving equilibrium within the emission bulb when the lamp is turned off, and this migration requires a time period of several weeks through several months. However, the change in the mercury vapor pressure within the emission bulb is not so great during a greater part of this time period, and it has been confirmed with an experiment using the absorption method, for example, that little change in the mercury vapor pressure within the emission bulb is observed after the first ten hours following turning on have elapsed. Furthermore, the mercury vapor pressure is generally determined by the composition of the principal amalgam which causes higher mercury vapor pressure than the auxiliary amalgam at the same temperature (see proceedings No. 7, 2000 Annual Conference of Illumination Engineering Institute of Japan).
The mercury emitted from the auxiliary amalgam near the electrode accompanying lighting is diffused toward the center of the discharge path of the emission bulb in several dozen seconds following the start of lighting, following which the mercury spreads generally all over the emission bulb generally in several minutes, and the desired mercury vapor pressure can be obtained. However, an excess of the mercury vapor pressure might be caused beyond the optimal range. Subsequently, thermal equilibrium is obtained for the entire lamp generally anywhere from around ten minute to one hour, and the mercury vapor pressure becomes constant dependent upon the temperature of the principal amalgam. At this time, the auxiliary amalgam reaches 100° C., and in some cases, reaches 200° C. or more, and accordingly, all the mercury is substantially emitted from the auxiliary amalgam (to be exact, metal such as indium (In) forming the auxiliary amalgam) to which the mercury has been absorbed.
However, it is difficult to increase the mercury vapor pressure speedily immediately following turning on so as to obtain the desired luminance even in a case of a fluorescent lamp including an auxiliary amalgam, and accordingly, further improvement of the light quantity rising property is desired.
On the other hand, with the bulb-shaped fluorescent lamp including a cooling portion at a part of the emission bulb thereof as shown in Japanese Unexamined Utility Model Registration Application Publication No. 61-63759, the heat capacity within the envelope is reduced due to further reduction of the size of the bulb-shaped fluorescent lamp, and accordingly, it is difficult to form the cooling portion at a portion of the exhaust pipe even in the event that the exhaust pipe is extended into the lighting device space by around 5 through 20 mm, where the compact and narrow space within the envelope practically kept airtight is separated by the partition.